To conduct a series of co-ordinated studies utilizing resistance hydrometry and partitional calorimetry designed to characterize the thermoregulatory system of the rhesus monkey (Macaca mulatta), and to evaluate its use as a viable model for temperature regulation studies which cannot be performed in man. Major emphasis will be placed on direct examination of the central and peripheral functional and biochemical adaptations in the thermoregulatory system of the rhesus monkey during heat acclimation in search of an answer to the following question: Is the increased sweating capacity at lower mean body temperature following heat acclimation due to: 1) an increase in the sensitivity of eccrine sweat glands, themselves, to thermal and neural stimuli; 2) a change in the gain or the set point temperature of the thermoregulatory centers in the hypothalamus to thermal inputs or 3) to a specific combination of 1, 2, and 3? This study will provide a better understanding of the basic physiological mechanisms of heat adaptation in higher primates, and as such may be directly applicable to man.